Wound Heat Exchanger

ABSTRACT

A capillary tube bundle sub-assembly for use in an extracorporeal heat exchanger includes a continuous capillary tubing wound about a core to define a plurality of capillary layers each including a plurality of capillary segments. The capillary segments each define opposing terminal ends adjacent opposing ends of the core. The capillary segments of each layer are circumferentially aligned relative to an axis of the core, with each successive layer being radially outward of an immediately preceding layer. The capillary segments are non-parallel with the axis, spiraling partially about the axis in extension between the opposing terminal ends. Each capillary segment forms less than one complete revolution (i.e., winds less than 360°). The segments within each layer are substantially parallel with one another; however, an orientation of the segments differs from layer-to-layer such as by pitch or angle.

BACKGROUND

The present disclosure relates to capillary tubing heat exchangers. Moreparticularly, it relates to capillary tube bundles useful inextracorporeal blood circuit heat exchangers, and related methods ofmanufacture.

Fluid-to-fluid heat exchangers are used in many different industries,and are typically constructed in conjunction with the intended end use.For example, a heat exchanger is an important component of anextracorporeal or cardiopulmonary bypass circuit. As a point ofreference, an extracorporeal blood circuit is commonly used duringcardiopulmonary bypass (i.e., a heart-lung bypass machine) to withdrawblood from the venous portion of the patient's circulation system andreturn the blood to the arterial portion. The extracorporeal bloodcircuit generally includes a venous line, a venous blood line reservoir,a blood pump, an oxygenator, a heat exchanger, an arterial line, andblood transporting tubing, ports, and connection pieces interconnectingthe components. The heat exchanger regulates a temperature of theextracorporeal blood as desired. For example, the heat exchanger can belocated upstream of the oxygenator and operated to cool the bloodarriving from the patient prior to oxygenation; alternatively, the heatexchanger can be operated to warm the extracorporeal blood.

Regardless of the direction of heat transfer between the heat exchangerand the patient's blood, extracorporeal blood circuit heat exchangersgenerally consist of metal bellows and a multiplicity of metal orplastic tubes (capillary tubes); a suitable heat exchange fluid, such aswater, is pumped through the tube lumens while the blood flows about thetube exteriors. The heat exchange fluid can be heated or cooled(relative to a temperature of the blood). As blood contacts the tubes,heat transfer occurs between the blood and the heat exchange fluid in anintended direction. Alternatively, blood flow can be through the tubelumens, with the heat exchange fluid flowing about the tube exteriors.

So as to have minimal impact on the circuit's prime volume, theextracorporeal heat exchanger is desirably as small as possible, whilestill providing high heat exchange efficiency. To meet theserequirements, the capillary tubes are micro-diameter or fiber-like(e.g., outer diameter no greater than about 0.05 inch). The heatexchange fluid is fluidly isolated from blood of the extracorporealcircuit by a wall thickness of the capillaries, keeping the fluidsseparate but allowing the transfer of heat from one fluid to the other.

A common capillary tubing format pre-assembles a large number of themicro-diameter tubes into a mat. The capillary tubes are knitted, wovenor otherwise held together with threads or stitching forming the warp ofthe mat. For heat exchanger applications, the capillary tube mat must bebundled together in some fashion to form a capillary tube bundle.Typically, the mat is wrapped or rolled around a core or mandrel. As themat is continuously wound about the mandrel, the mat wraps or winds ontoitself, resulting in a series of radially increasing layers. Thecapillary tubes of the mat are conventionally “biased” so that the tubesare not parallel with a width of the mat. Two layers of the mat withopposite bias angles can be simultaneously wound on the core to preventthe capillaries of subsequent layers from nesting in the gaps betweencapillary tubes of a preceding layer as the mat is wrapped onto itself.

While highly viable, capillary mat-based heat exchangers have certaindrawbacks. For example, capillary tubing mats are expensive due to thecomplexities of the knitting or weaving process. Further, the size,bias, materials, spacing, etc., of the capillary tubes is fixed, suchthat possible benefits available with varying one or more of theseparameters is unavailable.

Capillary tube bundles are also used in other mass transfer devices, andin particular blood oxygenators. As a point of reference, the capillarytubing employed with oxygenators is markedly different from that of heatexchangers; oxygenator capillary tubing is porous or semi-permeable,whereas heat exchanger capillary tubing is fluid impermeable. Thesedifferences affect fluid flow properties and may impact manufacturingtechniques. In any event, a woven capillary tube mat akin to the abovedescriptions can be used to form an oxygenator capillary tube bundle. Inan alternative approach, a single capillary tube, or ribbon of capillarytubes, is directly wound onto a rotating core, generating a helical windpattern. One such oxygenator bundle winding technique is set forth inU.S. Pat. No. 4,975,247 that otherwise describes the means by which towind an oxygenator capillary tube with specialized winding equipment.Regardless of whether such techniques are applicable to heat exchangercapillary tube bundles, the helical winding format of the '247 Patent(and other similar techniques) results in an interleaving of thecapillary tubes within each layer. In many instances, this interleavingmay be less than optimal for extracorporeal blood circuit heat exchangerfunctioning and performance.

In light of the above, a need exists for improved heat exchangercapillary tube bundle manufacturing techniques that combine low cost anddirect control over production, as well as for the capillary tubebundles and heat exchangers resulting from such techniques.

SUMMARY

Some aspects of the present disclosure relate to a capillary tube bundlesub-assembly for use in an extracorporeal blood circuit heat exchanger.The capillary tube bundle sub-assembly includes a substrate core and atleast one continuous capillary tubing. The core defines a cylindricalouter surface having a central longitudinal axis, a first core end, asecond core end opposite the first end, and a length between theopposing core ends in a direction of the central axis. The capillarytubing is wound about the outer surface to define a plurality of layersthat each include a plurality of capillary segments. The capillarysegments traverse at least a majority of the core length, with eachcapillary segment defining a first terminal end, adjacent the first coreend and a second terminal end adjacent the second core end. Thecapillary segments of each layer are circumferentially aligned relativeto the central axis, with each successive layer being radially outwardof an immediately preceding layer. An entirety of each of the capillarysegments is non-parallel with the central axis, spiraling partiallyabout the central axis in extension between the corresponding opposingterminal ends. In this regard, each capillary winds or segment wrapsabout the central axis by less than one complete revolution (i.e., windsless than 360°).

With so-constructed sub-assembly, the conventional capillary tube mat,and attendant cost, is eliminated, and the orientation (as well as otherparameters) of the capillary segments can be varied from layer-to-layer.This feature, in turn, facilitates optimized performance of a capillarytube bundle produced from the sub-assembly when employed as part of aheat exchanger, including heat transfer rates and pressure drop. In someembodiments, the capillary segments of each individual layer areparallel with one another, but an orientation of the capillary segmentsdiffers from layer-to-layer. For example, the capillary segments of afirst layer are oriented in a first pitch direction, whereas thecapillary segments of an immediately adjacent second layer are orientedin an opposite pitch direction. In related embodiments, the capillarysegments of the first layer are oriented at a first angle relative tothe central axis, whereas the capillary segments of the immediatelyadjacent second layer are oriented at a different, second angle. Withthese and other constructions, the capillary segments of immediatelyadjacent layers will not nest between each other. Further, by varying apitch or angle of the capillary segment between two (or more) layers, adesired packing fraction can be achieved, and can be selected tooptimize a desired shear rate of blood flow between the layers.

Yet other aspects in accordance with principles of the presentdisclosure relate to an extracorporeal blood circuit apparatus for heatexchanging. The apparatus includes a housing and a capillary tubebundle. The housing defines a blood flow path and a heat exchange fluidpath. The blood flow path is defined between a blood inlet and a bloodoutlet. The heat exchange fluid path is defined between a heat exchangeinlet and a heat exchange outlet. The capillary tube bundle is disposedwithin the housing, and includes a core and plurality of capillary tubesdisposed about an outer surface of the core. The capillary tubes definea plurality of layers, with the capillary tubes of each layer beingsubstantially circumferential aligned. Each successive layer is radiallyoutward of an immediately preceding layer. The tubes each have opposing,first and second open ends located adjacent corresponding ends of thecore, and traverse a majority of the length of the core. In this regard,each of the tubes is non-parallel with a central axis of the core, andspirals partially about the central axis by less than 360°. Anorientation (e.g., pitch direction, angle, etc.) of the tubes of a firstlayer differs from an orientation of the tubes of a second layer. Afirst band is disposed about the first open end of each of the capillarytubes, with the first open ends being fluidly open to the blood inlet orthe heat exchange inlet. A second band is disposed about the second openend of each of the capillary tubes, with the second open ends beingfluidly open to the corresponding blood outlet or heat exchange outlet.When assembled into an extracorporeal blood circuit, then, the apparatusoperates to effectuate heat exchange with the patient's blood in adesired direction. For example, a lower temperature liquid can be pumpedthrough the capillary tube lumens via the heat exchange fluid path;blood from the patient flows radially between the capillary tubes, withheat from the blood being thoroughly transferred to the heat exchangeliquid, thereby cooling the patient's blood.

Yet other aspects in accordance with principles of the presentdisclosure relate to a method of making a capillary tube bundle for usein a heat exchanger of an extracorporeal blood circuit apparatus. Themethod includes guiding a continuous capillary tubing in a firstdirection along an outer cylindrical surface of a core substrate to forma first capillary segment extending from a first terminal end adjacent afirst core end of the core to a second terminal end adjacent anopposing, second core end of the core. The first terminal end iscircumferentially offset from the second terminal end such that anentirety of the first capillary segment is non-parallel with a centralaxis of the core. Further, the first capillary segment traverses lessthan 360° of the outer surface. The continuous capillary tubing isfurther guided in a second direction opposite the first direction toform a second capillary segment immediately adjacent the first capillarysegment. The second capillary segment is formed to define opposing,first and second terminal ends. The so-formed first and second capillarysegments combine to form a portion of a first layer of capillarysegments substantially circumferentially aligned about the central axis.Finally, the continuous capillary tubing is guided in a reciprocatingfashion relative to the core to form a second layer of capillarysegments radially outward of the first layer. In some embodiments, apitch direction and/or angle of the capillary segments of the firstlayer differs from that of the capillary segments of the second layer,in yet other embodiments, the capillary tubing is guided to form amultiplicity of circumferential layers. In other embodiments, thecapillary segments are cut to form discrete, open-ended capillary tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a capillary tube bundle in accordance withprinciples of the present disclosure;

FIG. 1B is a cross-sectional view of the capillary tube bundle of FIG.1A, taken along the line 1B-1B;

FIG. 1C is a perspective view of the capillary tube bundle of FIG. 1A;

FIG. 2A is a side view of the capillary tubes provided with the bundleof FIG. 1A;

FIG. 2B is a magnified end view of a portion of the capillary tubes ofFIG. 2A;

FIG. 2C is a magnified side view of a portion of the capillary tubes ofFIG. 2A;

FIG. 3A is a simplified side view of a substrate winding core useful informing a capillary tube bundle sub-assembly in accordance withprinciples of the present disclosure;

FIG. 3B is an end view of the winding core of FIG. 3A;

FIGS. 4A and 4B are simplified side views illustrating initial stages ofwinding a capillary tube to the winding core;

FIG. 5A is a simplified side view illustrating further winding of thecapillary tubing, including formation of two capillary segments;

FIG. 5B is a simplified side view illustrating further winding of thecapillary tubing, including formation of a first layer;

FIG. 5C is a cross-sectional view of the arrangement of FIG. 5B, takenalong the line 5C-5C;

FIG. 6A is a simplified side view illustrating further winding of thecapillary tubing, including formation of a second layer over the firstlayer;

FIG. 6B is a cross-sectional view of the arrangement of FIG. 6A, takenalong the line 6B-6B;

FIG. 7A is a simplified side view of a winding device useful in formingthe capillary tubing sub-assembly of the present disclosure includingwrapping pins assembled to the winding core of FIG. 3A;

FIG. 7B is an end view of the device of FIG. 7A;

FIG. 7C is a simplified side view of the device of FIG. 7A, andincluding capillary tubing wound thereto in accordance with principlesof the present disclosure;

FIG. 8A is a simplified side view of a capillary tube bundlesub-assembly in accordance with principles of the present disclosure;

FIG. 8B is a simplified side view of a capillary tube bundle producedfrom the capillary tube bundle sub-assembly of FIG. 8A;

FIG. 9 is a simplified cross-sectional view of a heat exchangerapparatus in accordance with principles of the present disclosure,including the capillary tube bundle of FIG. 1A;

FIG. 10 is an exploded, perspective view of an extracorporeal circuitapparatus in accordance with principles of the present disclosure,including the capillary tube bundle of FIG. 1A; and

FIG. 11 is a simplified, cross-sectional view of the apparatus of FIG.10.

DETAILED DESCRIPTION

One embodiment of a capillary tube bundle 20 in accordance withprinciples of the present disclosure and useful as part of anextracorporeal blood circuit heat exchanger apparatus is shown in FIGS.1A-1C. The capillary tube bundle 20 includes a plurality ofmicro-diameter capillary tubes or heat transfer elements (schematicallyillustrated in FIGS. 1A-1C) 22, a core 24, and optional bands or caps 26a, 26 b. Details on the various components are provided below. Ingeneral terms, however, the capillary tubes 22 are formed about the core24 pursuant to the methodologies described below, including initialformation of a wound capillary tube bundle sub-assembly. The bands 26 a,26 b (where provided) serve to secure the capillary tubes 22 about thecore 24. The capillary tube bundle 20 can be employed in various end-useapplications, but is particularly useful as part of a heat exchanger orheat exchanger apparatus employed in an extracorporeal blood circuit. Insome embodiments, the capillary tube bundle 20 is connected within theextracorporeal blood circuit (or other environment requiring transfer ofheat between fluids) as part of a standalone heat exchanger apparatus;alternatively, the capillary tube bundles of the present disclosure canbe assembled to, or formed as part of a combination device, for exampleserving as the heat exchanger of a combination oxygenator and heatexchanger apparatus.

The capillary tubes 22 are micro-diameter tubes (e.g., hollowmicrofilaments or microfibers) as shown more clearly in FIGS. 2A-2C. Thecapillary tubes 22 are formed of a thermally conductive polymer ormetal, for example, polyethylene terephthalate (PET) or polyurethane.The capillary tubes 22 can have an outer diameter in the range of about0.010 inch to about 0.050 inch, and an inner diameter in the range ofabout 0.005 inch to about 0.030 inch, although other dimensions are alsocontemplated. The capillary tubes 22 are independent of one another, andare not interconnected by threads or stitching. As best shown in FIGS.2B and 2C, the capillary tubes 22 are arranged to define a plurality ofconcentric layers 28 a-28 c, with the capillary tubes 22 of each layer28 a-28 c being biased relative to the tubes 22 of an immediatelyadjacent layer 28 a-28 c.

An explanation of various features embodied by the capillary tube bundle20, such as the concentric layers 28 a-28 c of capillary tubes 22reflected in FIGS. 2A-2C, are best understood with reference to methodsof making the same in accordance with principles of the presentdisclosure. More particularly, aspects of the present disclosure relateto methods of forming a wound capillary tube bundle sub-assembly, aswell as subsequent processing of the sub-assembly to produce thecapillary tube bundle 20. With this in mind, FIGS. 3A and 3B aresimplified illustrations of a winding substrate core or mandrel 30 priorto application or formation of the capillary tubes 22 (FIG. 2A). As apoint of reference, the winding core 30 can be the core 24 (FIGS. 1A-1C)of the final capillary tube bundle 20 (FIGS. 1A-1C) and thus configuredfor use within a heat exchanger, or can be employed during manufactureof the capillary tube bundle sub-assembly and later replaced by the core24. Regardless, the winding the core 30 has or defines a cylindricalouter surface 32, and defines opposing first and second ends 34, 36. Thecylindrical shape of the core 30 defines a central longitudinal axis C,with a length L being defined between the core ends 34, 36 in adirection of the central axis C.

The capillary tubes 22 (FIG. 2A) are formed by initially applying(winding) one or more continuous lengths of capillary tubing 40 aboutthe outer surface 32 as initially reflected in FIG. 4A. In someembodiments, a plurality of continuous capillary tubings 40 can besimultaneously applied to the core 30 commensurate with the foregoingdescriptions; for ease of illustration, however, the followingexplanation provides a single one of the capillary tubing 40. Thecontinuous capillary tubing 40 is initially secured at a starting pointS to the outer surface 32 adjacent the first core end 34. For example,an adhesive, holding device (e.g., roller), friction, etc., can beemployed to maintain the capillary tubing 40 at or against the outersurface 32. The capillary tubing 40 is then traversed along the outersurface 32 in a partially spiral-like manner (i.e., non-parallel withthe central axis C). As shown in FIG. 4B, for example, the initial stageof winding includes extending the capillary tubing 40 from the startingpoint S to an end point E adjacent the second core end 36. As with thestarting point S, the end point E can be slightly spaced from the secondcore end 36. Further, the end point E can be established in thecapillary tubing 40 by various techniques, such as adhering thecapillary tubing 40 to the outer surface 32, a holding device (e.g.,roller), wrapping the capillary tubing 40 about a wrapping body or pinmounted to the winding core 30, friction, etc. Regardless, whentraversed in this manner, the applied capillary tubing 40 now defines afirst capillary segment 50 extending along the outer surface 32 (andheld in tension), with the starting and end points S, E effectivelydefining opposing first and second terminal ends 52, 54 of the firstcapillary segment 50 adjacent the first and second core ends 34, 36,respectively. The first capillary segment 50 traverses at least amajority of the core length L. The opposing terminal ends 52, 54 arecircumferentially offset from one another, such that the first capillarysegment 50 is non-parallel with the central axis C of the winding core30. An orientation of the first capillary segment 50 in extension fromthe first terminal end 52 to the second terminal end 54 serves to definea pitch direction and angle of the first capillary segment 50 relativeto the central axis C. Notably, while the first and second terminal ends52, 54 are circumferentially offset from one another (such that thefirst capillary segment 50 is characterized as partially spiraling aboutthe cylindrical outer surface 32), partial spiraling of the firstcapillary segment 50 does not make a full revolution about the centralaxis C. That is to say, the first capillary segment 50 winds less than360° about the central axis C in extension from the first terminal end52 to the second terminal end 54, and thus does not define a completehelix.

With the second terminal end 54 of the first capillary segment 50 nowestablished relative to the outer surface 32, winding of the capillarytubing 40 continues as shown in FIG. 5A, with the capillary tubing 40being transversed along the outer surface 32 in an opposite direction,extending from the second terminal end 54 of the first capillary segment50 toward the first core end 34. At a location generally aligned withthe first terminal end 52 of the first capillary segment 50, butcircumferentially offset therefrom, the continuous capillary tubing 40is held (in tension) relative to the outer surface 32 commensurate withprevious descriptions. This winding pattern thus establishes a secondcapillary segment 60 having a first terminal end 62 adjacent the firstcore end 34, and a second terminal end 64 adjacent the second core end36. Due to the continuous nature of the capillary tubing 40, the secondterminal ends 54, 64 of the first and second capillary segments 50, 60are commonly formed or shared. Stated otherwise, a turnaround 70 isestablished in the wound capillary tubing 40, and the segments 50, 60remain integral or homogenous parts of a continuous capillary tube.

In some embodiments, the circumferential offset (i.e., circumferentialarc length) between the first and second terminal ends 52, 54 of thefirst capillary segment 50 corresponds with the circumferential offsetbetween the first terminal ends 52, 62 of the first and second capillarysegments 50, 60. With this construction, then, the second capillarysegment 60 is substantially parallel with the first capillary segment 50(e.g., within 5° of a true parallel relationship). Alternatively,arrangement or orientation of the second capillary segment 60 need notbe substantially parallel with the first capillary segment 50.Regardless, extension of the second capillary segment 60 between thecorresponding first and second terminal ends 62, 64 is non-parallelrelative to the central axis C, and winds about less than 360° of theouter surface 32.

Continued tensioned winding of the capillary tubing 40 progresses in asimilar fashion, with the capillary tubing 40 being continuouslytraversed along the cylindrical surface 32, reciprocating betweencircumferentially offset locations adjacent the first and second coreends 34, 36. As shown in FIG. 5B and 5C, additional capillary segmentsare thusly formed, each having an orientation in extension betweencorresponding opposing terminal ends that can be substantially parallelto the first and second capillary segments 50, 60 described above. Inthe side view of FIG. 5B, the additional capillary segments 80-92 arevisible, with the cross-sectional view of FIG. 5C showing all of thecapillary segments. At the intermediate stage of winding reflected inFIGS. 5B and 5C, a first layer 100 of capillary segments is generated.As best illustrated in FIG. 5C, the first layer 100 is characterized byeach of the corresponding capillary segments commonly designated by “A”in the figures) being substantially concentric about the central axis Cor substantially circumferentially aligned with one another relative tothe central axis C (e.g., within 5% of a true concentric arrangement orcircumfrential alignment). Because the first layer capillary segments Aeach traverse less than 360° of the outer surface 32, the segments A donot interleave with one another in defining the first layer 100. It willbe recalled that two or more continuous capillary tubings 40 can besimultaneously wound and will collectively form the first layer segmentsA. Regardless, each of the first layer segments A are continuous withanother of the first layer segments A, and the terminal ends of eachsegment A are fluidly closed.

Reciprocating winding of the continuous capillary tubing 40 continuesfurther, generating additional capillary layers radially outward of thefirst layer 100. FIGS. 6A and 6B reflect further tensioned winding ofthe capillary tubing 40 about the winding core 30 to form a second layer110. The second layer 110 is radially outward of, but in contact with,the first layer 100. Solely for purposes of explanation, portions of thecapillary tubing 40 wound onto the first layer 100 are illustrated withstippling so as to more clearly distinguish the added capillary tubingof the second layer 110 from that of the first layer 100. The secondlayer 110 is composed of a plurality of capillary segments (generallyreferenced at “B” in the figures). The second layer capillary segments Bare akin to the first layer capillary segments A in that each of thesecond layer capillary segments B extends between opposing, first andsecond terminal ends 112, 114 (identified for the second layer capillarysegment B1) that are otherwise located adjacent the first and secondcore ends 34, 36, respectively. Further, the second layer capillarysegments B are non-parallel with the central axis C, and partiallyspiral about the central axis C less than 360° (less than one completerevolution) as described above. However, the orientation of the secondlayer capillary segments B differs from that of the first layercapillary segments A.

In some embodiments, a pitch direction of the second layer capillarysegments B is opposite the pitch direction of the first layer capillarysegments A. For example, each of the first layer capillary segments Acan be described as having a left hand pitch direction in extension fromthe corresponding first terminal end to the corresponding secondterminal end, whereas the second layer capillary segments B each have aright hand pitch direction in extension from the corresponding firstterminal end to the corresponding second terminal end. Alternatively orin addition, an angle of each of the second layer capillary segments Brelative to the central axis C is different from the angle definedbetween the central axis C and each of the first layer capillarysegments A. Due to the differing pitch direction and/or angle, thesecond layer capillary segments B do not nest between the first layercapillary segments A. A purpose of the opposing biases or pitchdirections is to prevent any nesting of the capillary segments A, Bbetween the two layers 100, 110, which could result in increasedresistance to liquid flow (e,g., blood flow), and undesirable andunpredictable shear on the liquid (e.g., blood) flowing therethrough(i.e., between the capillary segments). Alternatively, the capillarysegments A, B can have other angles or biases relative to the centralaxis C.

To facilitate a better understanding of the layer-to-layer pitchdirection and/or angle differences, it may be helpful to refer topredefined winding turnaround locations established along the core outersurface 32 in accordance with principles of the present disclosure. Forexample, FIGS. 7A and 7B illustrate, in simplified form, wrapping pins120, 122 assembled to, and extending outwardly from, the outer surface32 of the core 30 adjacent the ends 34, 36, respectively. For ease ofexplanation, relative to the orientation of FIG. 7A, the wrapping pins120 adjacent the first core end 34 are referred to as “upper” wrappingpins, and the wrapping pins 122 adjacent the second core end 36 arereferred to as “lower” wrapping pins, it being understood that thewinding core 30 need not be vertically oriented during the windingprocess. With this in mind, FIGS. 7A and 7B illustrate twelve of theupper wrapping pins 120 a-120 l and twelve of the lower wrapping pins122 a-122 l, although any other number is also acceptable.

Respective ones of the wrapping pins 120 a-120 l, 122 a-122 l arelongitudinally aligned with one another, and the wrapping pins 120 a-120l, 122 a-122 l serve as turnaround locations during winding of thecontinuous capillary tubing 40 as shown in FIG. 7C. With this in mind,the angle of each of the first layer capillary segments A (relative thecentral axis C) is dictated by extending the continuous capillary tubing40 from one of the upper wrapping pins 120 a-120 l to thecircumferentially “next” layer wrapping pin 122 a-122 l (or vice-versa).For example, with respect to the first layer capillary segmentidentified at A1 in FIG. 7C, the segment A1 extends from the first upperwrapping pin 120 a to the second lower wrapping pin 122 b (i.e.,relative to the orientation of FIG. 7C, the segment A1 extends in aclockwise direction). The second layer capillary segment identified atB1 not only extends from the first upper wrapping pin 120 a in acounterclockwise direction, but terminates at the eleventh lowerwrapping pin 122 k. By effectively “skipping” the twelfth lower wrappingpin 122 l, the second layer capillary segment B1 is oriented at an anglediffering from that of the first layer capillary segment A1. Winding ofthe continuous capillary tubing 40 in forming the second layer 110 (FIG.6B) follows this same pattern, dictating that all of the second layercapillary segments B are oriented differently from the first layercapillary segments A.

Winding of the continuous capillary tubing 40 continues further in asimilar fashion, generating additional, radially outward layers, eachconsisting of a plurality of capillary segments that are substantiallycircumferentially aligned relative to the central axis C, non-parallelwith the central axis C, and partially spiraled about the central axis Cby less than 360°. An orientation (e.g., pitch direction, angle, etc.)of the capillary segments differ from layer-to-layer to impedeinterlayer nesting as described above. Other variables can be introducedduring the winding process. For example, in addition or as analternative to varying the pitch direction or angle, the number ofcapillary segments within a particular layer can be varied. Thecapillary tubing itself can be varied from one layer to the next, forexample by employing capillary tubing having a different inner and/orouter diameter with different ones of the capillary layers. Thesevariations, in turn, can effectuate a desired packing fraction in theresultant capillary tube bundle 20 (FIG. 1A). For purposes of thisdisclosure, packing fraction is defined to mean the fraction of a unitvolume of bundle space occupied by capillary tubing segments. Thepacking fraction can be determined in ways known in the art, includingthe conventional method of measuring the interstitial space between thecapillary segments by weight gain when a unit volume is primed with aknown liquid. Packing fraction in a particular region or zone locatedradially outward may be determined by stopping the corresponding windingprocess at the radially inner radial boundary of the region or zone anddetermining the zone at that stage, and then continuing the windingprocess to the outer radial boundary of the region or zone indetermining the zone or fraction at that stage. Computations known inthe art will determine the packaging fraction of the region or zoneusing the prior to values.

Once a desired number of capillary layers have been wound to the windingcore 30, the winding process is complete, resulting in a capillary tubebundle sub-assembly 150 is illustrated in FIG. 8A. The number of layersprovided with the final capillary tube bundle sub-assembly 150 can beselected in accordance with a desired end performance. In thesub-assembly form, the continuous capillary tubing 40 is stillcontinuous such that none of the capillary segments (referencedgenerally at 152) are exteriorly open (other than, perhaps, at theopposing ends of the continuous capillary tubing 40). To facilitate useas part of a heat exchanger, the capillary segments 152 each must thenbe opened at the corresponding opposing terminal ends, for example via acutting procedure. For example, the optional bands 26 (FIG. 1A) areapplied to the wound capillary tubing 40 so as to maintain the tensionin the capillary segments 152. The capillary segments 152 are then cut(e.g., a conventional hot knife) at locations proximate the opposingterminal ends 154, 156 (identified for one of the capillary segments 152a in FIG. 8A). The fluidly closed or continuous terminal ends 154, 156of each of the capillary segments 152 are thus removed or otherwiseopened relative to the capillary lumen, resulting in the discretecapillary tubes 22 identified generally in FIG. 8B, with each capillarytube 22 extending between opposing, first and second open ends 160, 162(identified for one of the capillary tubes 22 a in FIG. 8B). Optionally,the ends 160, 162 can be embedded in a solidified potting compound asknown to those of ordinary skill. Stated otherwise, the cutting process(and optional potting process) transitions the capillary tube bundlesub-assembly 150 of FIG. 8A to the capillary tube bundle 20 of FIG. 8B.The capillary tubes 22 are essentially identical to the capillarysegments 152 (FIG. 8A) described above, except that the continuousterminal ends no longer exist. The capillary tubes 22 form the pluralityof concentric layers previously described, and each extend non-parallelwith the central axis C and partially spiral (less than 360°) about thecentral axis C. Notably, the capillary tube bundle 20 does not includethreads or stitching interconnecting the capillary tubes 22 as otherwisefound with conventional mat-based heat exchanger bundles. Further,commensurate with the above descriptions, a variable packing fraction orother variations can be incorporated into the bundle 20. The capillarytube bundle 20 can then be assembled with other components to form aheat exchanger.

While the above-described methods of forming the capillary tube bundlesub-assembly 150 includes winding the capillary tubing about wrappingpins embedded into the winding core 30, other techniques are alsocontemplated. For example, continuous winding equipment can be used,including a fiber guide that moves the capillary tubing 40 (FIG. 5B), ora ribbon of capillary tubings 40, in a reciprocating fashion relative tothe winding core 30, along with a rotational mounting member thatrotates the winding core 30 relative to the fiber guide. With thisconstruction, the winding core 30 is continuously rotated withreciprocating movement of the fiber guide, but rotates less than 360°during each traversing movement of the fiber guide. In otherembodiments, the winding core 30 can be elongated. During subsequentcutting operations, the sub-assembly 150 (FIG. 8A) is severed at one ormore intermediate locations to create two (or more) capillary tubebundles 20 from a single sub-assembly 150. In related embodiments, thesegments 152 of the elongated sub-assembly 150 can traverse more than360°, with the final capillary tube bundles 20 being cut at longitudinallocations where the resultant tubes 22 wrap less than 360°.

In some constructions, the winding core 30 about which the capillarytubing 40 (FIG. 5B) is wound is configured for assembly and use within aradial flow-type heat exchanger apparatus. In other embodiments, thecapillary tube bundle sub-assembly 150 (or the capillary tube bundle 20)can be removed from the winding core 30 and assembled over a separatecore specifically designed for a particular heat exchanger. As shown inFIG. 1B, then, the heat exchanger core 24 can assume a variety of forms,and generally defines an inlet 200, a central passageway 202, and one ormore outlet openings 204. The inlet 200 is fluidly open to thepassageway 202, as are the outlet openings 204. With embodiments inwhich the resultant heat exchanger apparatus is intended to impart aradially outward flow pattern onto liquid flowing through the passageway202 (and otherwise entering the passageway 202 via the inlet 200), theopenings 204 can be formed along an inner portion of the core 24,projecting through a wall thickness thereof. Other locations for theoutlet opening(s) 204 are equally acceptable. As a point of reference,the term “heat exchanger” is a component including the capillary tubebundle 20 and the heat exchanger core 24. The so-defined heat exchangercan be utilized as part of a standalone, finished heat exchangerapparatus or device that otherwise includes an outer housing and variousfluid ports. Alternatively, the so-defined heat exchanger can serve as asubassembly component of a combination extracorporeal blood circuitapparatus or device that performs heat exchange and one or moreadditional functions.

One example of a heat exchanger apparatus 210 is constructed with thecapillary tube bundle 20 by assembling the bundle 20 within a housing220 as generally reflected in FIG. 9. The housing 220 can assume variousforms, and generally includes or defines a chamber 222 sized to receivethe capillary tube bundle 20, a blood inlet 224, a blood outlet 226, aheat exchange inlet 228, and a heat exchange outlet 230. Withembodiments in which the heat exchanger apparatus 210 functions byforcing heat exchange fluid through the lumens of the capillary tubes 22(drawn schematically), the blood inlet 224 is fluidly connected to thecentral passageway 202 of the core 24. The blood outlet 226 is fluidlyconnected the chamber 222 radially opposite the capillary tube bundle20. The heat exchange inlet 228 is fluidly connected to the first openends (or inflow ends) 160 of the capillary tubes 22, whereas the heatexchange outlet 230 is fluidly connected to the second open ends foroutflow ends) 162 of the capillary tubes 22.

When the heat exchanger apparatus 210 is assembled as part of anextracorporeal blood circuit, blood flow from the patient is introducedat the blood inlet 224. Heat exchange liquid is introduced at the heatexchange inlet 228. The heat exchanger apparatus 210 may either heat orcool the blood flowing through the heat exchanger apparatus 210. Sincehypothermia may be caused during cardiac surgery (especially in infantand pediatric surgeries) to reduce oxygen demand, and since rapidre-warming of the blood undesirably produces bubble emboli, the heatexchanger 210 is generally used to gradually re-warm blood and preventemboli formation. The heat transfer medium used in the heat exchangerapparatus 210 can comprise water or other suitable fluids. FIG. 9includes arrows (labeled as “fluid) that shows the flow of a heatexchange medium through the heat exchanger apparatus 210, and inparticular the capillary tubes 22, with entry at the heat exchange inlet228 and exit at the heat exchange outlet 230. After flowing through thecore passageway 202, blood moves sequentially radially outwardly throughthe capillary tubes 22. The direction of blood flow is directed byarrows (labeled as “blood”),

In yet other embodiments, the capillary tube bundle 20 (and core 24) canbe a heat exchanger incorporated into or as part of other fluid handlingapparatuses or devices performing functions in addition to heatexchange. For example, FIG. 10 illustrates a combination oxygenator andheat exchanger apparatus 300 incorporating the capillary tube bundle 20described above. The apparatus 300 further includes an oxygenator 302and various housing components (referenced generally at 304 a-304 c).The oxygenator 302 can assume any form known in the art, as can thehousing components 304 a-304 c. For ease of illustration, FIG. 10illustrates the core 24 apart from the capillary tubes 22 (referencedgenerally). In other embodiments, the apparatus 300 can include aseparate supportive core over which the heat exchanger core 24 isdisposed.

FIG. 11 shows, in simplified form, fluid flow through the apparatus 300.A heat transfer medium flows through the heat exchanger capillary tubebundle 20 as shown by the arrows “fluid”. After flowing through the heatexchanger capillary tube bundle 20, blood moves sequentially andradially outwardly and through the oxygenator 302 that is otherwisearranged around the heat exchanger capillary tube bundle 20. Thedirection of blood flow is indicated by arrows labeled as “blood”. FIG.11 also includes arrows that show the flow of an oxygen-containingmedium through the oxygenator 302 (labeled as “gas”). The oxygenator 302may concentrically surround the heat exchanger capillary tube bundle 20(e.g., as one or more continuous micro porous fibers). It will beunderstood that the heat exchanger capillary bundle 20 of the presentdisclosure can be incorporated into a plethora of other apparatuses thatmay or may not include the oxygenator 302.

The capillary tube bundles, capillary tube bundle sub-assemblies, andmethods of manufacturing thereof, of the present disclosure providemarked improvements over existing devices and methods. By allowing heatexchanger manufactures to select one or more characteristics of thewound capillary tube(s) during winding, heat exchanger capillary bundlesof the present disclosure exhibit reduced costs, controlled packingfraction, and optionally variable capillary diameters.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand scope of the present disclosure.

1-13. (canceled)
 14. An extracorporeal blood circuit apparatus forperforming heat exchange comprising: a housing defining: a blood flowpath from a blood inlet to a blood outlet, a heat exchange fluid pathwayfrom a heat exchange inlet to a heat exchange outlet; a capillary tubebundle disposed within the housing and including: a core defining acylindrical outer surface having a central axis, a first core end, asecond core end opposite the first core end, and a length between thecore ends in a direction of the central axis, a plurality of capillarytubes disposed about the outer surface to define a plurality ofcapillary layers, wherein: the capillary tubes of each layer aresubstantially circumferentially aligned relative to the central axis andeach successive layer is radially outward of an immediately precedinglayer, each of the capillary tubes is non-parallel with the centralaxis, traversing a majority of the core length from a first open endadjacent the first core end to a second open end adjacent the secondcore end, each of the capillary tubes spirals partially about thecentral axis in extension from the corresponding first open end to thecorresponding second open end by less than 360°, an orientation of thecapillary tubes in a first one of the layers differs from an orientationof the capillary tubes in a second one of the layers; a first banddisposed about the first open end of each of the capillary tubes, thefirst open ends being fluidly open to one of the blood net and the heatexchange inlet; and a second band disposed about the second open end ofeach of the capillary tubes, the second open ends being fluidly open toone of the blood outlet and the heat exchange outlet.
 15. The apparatusof claim 14, wherein the second layer is disposed against the firstlayer opposite the outer surface.
 16. The apparatus of claim 15, whereinthe capillary tubes of the first layer have a pitch direction inextension from the corresponding first open end to the correspondingsecond open end, and the capillary tubes of the second layer have asecond pitch direction in extension from the corresponding first openend to the corresponding second open end, the first pitch directionbeing opposite the second pitch direction.
 17. The apparatus of claim16, wherein the capillary tubes of the first layer are arranged at aright hand pitch and the capillary tubes of the second layer arearranged at a left hand pitch,
 18. The apparatus of claim 15, whereinthe capillary tubes of the first layer are substantially parallel withone another in extension from the corresponding first open end to thecorresponding second open end.
 19. The apparatus of claim 15, whereineach of the capillary tubes of the first layer are arranged at a firstangle relative to the central axis and each of the capillary tubes ofthe second layer are arranged at a second angle relative to the centralaxis, the first angle being different from the second angle.
 20. Theapparatus of claim 14, wherein the capillary tube bundle ischaracterized by the absence of a thread interconnecting each of thecapillary tubes of the first layer.
 21. The apparatus of claim 14,wherein the core forms a central passageway and radial openings from thecentral passageway to the outer surface, the central passageway beingfluidly connected to the blood net to establish a radial flow of bloodthrough the layers.
 22. The apparatus of dam 21, wherein the first openends are fluidly connected to the heat exchange net and the second openends are fluidly connected to the heat exchange outlet, and furtherwherein when connected to an extracorporeal blood circuit, the heatexchanger is configured to direct blood flow from the blood net andradially between the plurality of capillary tubes, and further to directheat exchange fluid through a lumen of each of the capillary tubes. 23.A method of making a capillary tube bundle for use in a heat exchangerof an extracorporeal blood circuit apparatus, the method comprising:guiding a continuous capillary tube in a first direction along an outercylindrical surface of a core substrate to form a first capillarysegment extending from a first terminal end adjacent a first core end ofthe core to a second terminal end adjacent an opposing, second core endof the core, wherein the first terminal end is circumferentially offsetfrom the second terminal end such that an entirety of the firstcapillary segment is non-parallel with a central axis of the core, andthe first capillary segment traverses less than 360° of the outersurface; guiding the continuous capillary tubing in a second directionopposite the first direction to form a second capillary segmentimmediately adjacent the first capillary segment, the second capillarysegment including opposing, first and second terminal ends; wherein thefirst and second capillary segments combine to form a portion of a firstlayer of capillary segments substantially circumferentially alignedabout the central axis; and guiding the continuous capillary tubing in areciprocating fashion relative to the core to form a second layer offiber segments radially outward of the first layer.
 24. The method ofclaim 23, wherein the capillary tubing continuously forms secondterminal ends of the first and second capillary segments at a turnaroundpoint.
 25. The method of claim 23, wherein the first and secondcapillary segments are substantially parallel.
 26. The method of claim23, wherein the capillary segments of the first layer extend in a firstpitch direction, and the capillary segments of the second layer extendin a second pitch direction opposite the first pitch direction.
 27. Themethod of claim 23, wherein a circumferential offset of the first andsecond terminal ends of each of the capillary segments of the firstlayer differs from a circumferential offset of the first and secondterminal ends of each of the capillary segments of the second layer. 28.The method of claim 23, wherein the steps of guiding the continuouscapillary tubing include: reciprocating a fiber guide relative to thecore; and rotating the core simultaneously with reciprocating movementof the fiber guide, wherein the core is rotated less than 360° duringeach traversing movement of the fiber guide.
 29. The method of claim 23,further comprising: cutting each of the capillary segments adjacent thecorresponding first and second terminal ends to fluidly open each of thecapillary segments and form a plurality of discrete capillary tubes.